This invention is directed generally to the area of circuit monitoring, sand more particularly to a novel and improved system for monitoring power signals in a power circuit, such as a residential or industrial, or aircraft power circuit.
The art of power circuit monitoring continues to develop. Long standing monitoring systems, for example for residential use, have in the past consisted of nothing more sophisticated than fuses, and more commonly, circuit breakers which have a given power/time characteristic so that the circuit is broken or switched to an open circuit condition, usually at a power distribution center or breaker box, when the current through the protected line exceeds the power/time characteristic of the circuit breaker or fuse component or the like. In many applications, and in particular in residential kitchen and bathroom applications, it has become common to provide a circuit breaker as part of an electrical outlet, such that the outlet is protected from current or voltage spikes. This again is commonly done with circuit breaker components which react to current spikes or time/current characteristics to open the circuit to the outlet. This removes power from the outlet and any appliances or other electrically powered equipment plugged into the outlet or merely from the outlet itself in the case of inadvertent contact with some foreign object or the like. In some instances, various appliances for home use are provided with circuit breaker-equipped power cords, which operate similarly to the circuit breaker outlet.
More recently still, arcing fault protection has become a consideration in the design of both residential and industrial electrical systems, as well as in aircraft electrical systems. In the case of arcing fault protection, a number of systems have been devised for reliably detecting arcing faults, and distinguishing these from normal arcing occurrences in some loads such as motors or the like, to prevent false trips as much as possible. Arcing faults generally fall into two categories, series and parallel. Series arcs generally occur when there is a break or fault in a conductor, and arcing develops across the break or fault as current continues to flow and potential builds up thereacross. In parallel arcing, arcing occurs between phase lines of a multi-phase power system or between one or more of phase lines and ground, in a single phase or multi-phase system. This may occur, for example, when the insulation of conductors becomes broken or damaged in some manner. Systems have been developed by Square D Company, the owner of this application, to reliably detect arcs of both types, as well as ground faults and other electrical faults, and to provide systems to rapidly and reliably trigger or trip circuit breakers in response to such electrical faults. Power monitoring systems include systems for mounting at power distribution centers or breaker boxes, as well as systems which can be mounted at individual outlets to provide protected outlets. Power monitoring systems may also be associated with appliances, for example, built in to appliance cords or electrical connectors affixed to the end of appliance cords, as well as in junction boxes, dimmer switches, smoke detectors and other electrical equipment. Square D Company has also provided and/or proposed novel and useful fault protection systems for use in aircraft for detecting and protecting against arcing faults, ground faults and other electrical faults.
In our currently proposed power monitoring systems for use in such electrical fault protection systems, generally speaking, a monitoring circuit is provided which utilizes a processor to process digital signals which are related to power signals detected by various sensors on one or more power lines to be monitored. Heretofore, circuit monitoring systems have been provided in various forms, however, usually integrated into a single monitoring apparatus contained in a single housing. However, with increasing regulatory requirements upon the performance of circuit monitoring systems, it may become necessary to provide for calibration of various circuit components of a system, so as to maintain metering accuracy. The testing and calibration of a circuit monitoring system installed in the field may be a difficult proposition. While a circuit monitoring system may be factory calibrated, it is difficult to easily and simply retest and recalibrate the system, if necessary, in the field. Such testing and monitoring would require shutting down the circuit monitoring system for some period of time, thus, correspondingly either shutting down power on the lines being monitored or providing unmonitored, unprotected service during the period of testing. Neither of these options is particularly attractive or acceptable.